In order to compress a composition into tablets, lubrication of the tabletting machinery is generally required. Although it is possible to lubricate the dies and presses directly (external lubrication), the problems involved when tablets are to be prepared commercially at a high speed makes their use impractical. Therefore, most lubricants used are added to the formulation itself (internal lubrication). When a lubricant is added to the formulation, it must provide the necessary lubrication without interfering with the flowability or compressability of the formulation and without interfering with the release of the active ingredient. Many of the best lubricants are hydrophobic or water insoluble, for example calcium or magnesium stearate, talc, and vegetable oils; and for many formulations where rapid release of the active ingredient is not required, these lubricants are sufficient. However, lubrication of tablets where rapid dissolution is desired presents a particular problem, since hydrophobic lubricants may impede the release of the active ingredient(s) from the tablet. When the tablet is a pharmaceutical, this release of the active ingredient may be crucial to the onset of action and even to whether the ingredient elicits the desired response. In addition, when a tablet intended for dissolution in water prior to ingestion is prepared, e.g. an effervescent tablet, hydrophobic lubricants are generally avoided because their presence tends to leave an unsightly scum upon dissolution making the solution less palatable to the consumer. Therefore, there is a need for water soluble lubricants which may be used in general, but in particular for tabletting fast dissolving pharmaceuticals and/or nutritional supplements.
Although water soluble lubricants do not impede the release of active ingredient(s) from the tablet as hydrophobic lubricants can, they generally have poorer lubrication properties than the hydrophobic lubricants. Therefore, there has been a proliferation of compositions and processes providing soluble lubricants. Known soluble lubricants include: fumaric acid, adipic acid, boric acid, sodium benzoate, potassium benzoate, sodium propionate, sodium stearyl fumarate, sodium lauryl sulfate, magnesium lauryl sulfate, L-leucine and various polyethylene glycols ranging in (average) molecular weight from 4000 to 20000. There have been a number of patents related to lubricants for tabletting pharmaceuticals or nutritional supplement, including U.S. Pat. Nos. 3,566,491; 3,548,099; 3,518,346; 3,506,756; 3,518,343; 3,518,344; 3,518,345; 3,619,462; 3,577,490; and 3,577,492. Some of the lubricant formulations provided herein were disclosed in a copending patent applications containing inventions by the same inventor. This copending patent application was published on Sep. 30, 1992 as EP 0 505 872 A1.
In practice, all known soluble lubricants have significant limitations. The new lubricant(s) and lubricant formulation(s) provide herein have fewer such limitations.